Features of a Gaussian beam near-field diffraction upon variations in the relief height of subwavelength silicon optical elements

Features of the near-field diffraction of Gaussian beams and Laguerre-Gauss modes by silicon subwavelength optical elements with varying relief height were studied in this paper using a finite-difference time-domain method. Diffractive axicons and subwavelength ring gratings were consid-ered as the optical elements with varying relief height. It was shown that the height of individual rings of the ring grating relief can be selected in such a way that the focal spot size is reduced to $0.26\lambda$, an extended intensity line of length up to $4.88\lambda$ is generated and optical traps are formed.